The present invention relates to a monitoring device used for the monitoring of an area of building or land.
Such a monitoring device comprises at least one light waveguide used as a sensor.
The present invention also relates to:                a monitoring system comprising such a monitoring device, and        a related monitoring method.        
The technical field of the invention concerns more specifically the field of the monitoring of deformation of building structures.
It is known in the prior art a monitoring device used for the monitoring of an area of building or land, and comprising                an optical strand used as a sensor, placed in or on an area to monitor, consisting in a component as described in document EP 0 264 622 B1, with optical waveguides that are prestressed to such an extend that they are subjected to tensile stress even when subjected to little deformation.        one optical source for emitting an optical emission signal transmitted in the optical strand;        one optical analogue detector for detecting monitoring data comprising an intensity of an optical return signal corresponding to the optical emission signal returning from the optical strand; and        processing means for calculating a deformation of the monitored area from the detected monitored data.        
The optical strand is described in details in documents EP 0 264 622 B1 and U.S. Pat. No. 5,044,205. Said document concerns indeed a component with optical waveguides which serve to monitor the deformations of the component and are fastened on or in the component under mechanical prestress, the optical waveguides being firmly bounded to the component over at least part of its length and being prestressed to such an extent that they are subjected to tensile stress even when deformations due to compression, shrinkage or creep occur in the component.
Also from EP 0 264 622 B1, the man skilled in the art knows a method for the monitoring of deformation of a building structure with the optical strand. The optical strand is connected to a measuring apparatus. The forces applied on the optical strand have the effect of dampening light sent through the optical strand in a manner which varies according to the intensity of these forces. By detecting the attenuation of the light, a measurement of the elongation of the optical strand with respect to his nominal length is obtained indirectly from a characteristic curve. Said elongation can be related to a deformation of the monitored building structure.
According to the prior art, the optical source, the optical analogue detector and the processing means are placed in a remote station connected with said optical strand using optical fibers.
A drawback of such a monitoring device is that it can be expensive.
Another drawback of such a monitoring device is that it can be fragile.